Micro-Electro-Mechanical Systems, or MEMS can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have a mechanical functionality. Since MEMS devices are created with the same tools that are used to create integrated circuits, micromachines and microelectronics can be fabricated on the same piece of silicon to enable machines with intelligence.
MEMS structures can be applied to quickly and accurately detect very small displacements, for example in inertial sensors. For example, in an accelerometer a mass suspended on a spring structure to the body of the device may be displaced proportional to the acceleration of the device, and these displacements of the mass are detected. As a solid object, the mass-spring structure typically has a resonant frequency in which it exhibits resonance or resonant behavior by naturally oscillating at some frequencies, called its resonant frequencies, with greater amplitude than at others. In these resonant frequencies the displacement is much larger than in other frequencies, which causes overload that disturbs the detection in the miniaturized dimensions of MEMS structures.
These disturbances are typically eliminated by damping of the detected motion. A conventional method has been to use passive gas damping, but for many applications gas damping is too non-linear and causes too many disadvantageous effects to the operation of the system. In some configurations, like vibrating gyroscopes, gas damping is not even applicable, because damping to the resonant excitation of primary vibration must be kept low.
In feed-back damping, or active damping, the detected displacement is monitored and a relative force is generated to oppose the motion. In known systems, active damping has been implemented with a closed feed-back loop that comprises a differentiator and a transducer responsive to the differentiator signal. A differentiator has many properties due to which it is well suited to control damping of displacements in mechanical resonators. The problem is, however, that structures are very seldom ideal, and in real-life resonators there are additional mechanical resonance modes. When the differentiator output signal is amplified to generate an appropriately high damping force, the feed-back-loop easily starts to oscillate disruptively.